1. Field of the Invention
This invention relates to a method and an apparatus for decoding a Transport Format Combination Indicator (TFCI) inserted into a radio frame, in a mobile communications system using a Wideband-Code Division Multiple Access (hereinafter referred to as W-CDMA) system.
The present invention also relates to a mobile station apparatus and a base station apparatus, which include the above decoding method and the above decoding.
The present invention further relates to a method which is used for multiplexing information in mobile communications and which is suitable for the above decoding method.
2. Description of the Related Art
One method used in current mobile communications field is a method of multiplexing different pieces of information such as audio and packet having different qualities of service (hereinafter referred to as QoS) into a same radio frame and then transporting the frame through a radio circuit. One of such methods is known as a W-CDMA method being studied by a Third Generation Partnership Project (hereinafter referred to as 3GPP).
FIG. 9 shows an exemplary state of a plurality of pieces of information being multiplexed in accordance with the W-CDMA method. As shown in FIG. 9, one radio frame has a length of 10 milliseconds (hereinafter referred to as msec) and may multiplex a plurality of pieces of information in each radio frame.
The W-CDMA method used in FIG. 9 may select and set a Transmission Time Interval (hereinafter referred to as TTI and which represents the shortest time length during which data may be decoded) for each of a plurality of pieces of information to be multiplexed, out of predetermined four kinds of TTIs. The four kinds of TTIs to be selected include 10 msec, 20 msec, 40 msec and 80 msec. In a case of FIG. 9, information A has a TTI of 10 msec, information B has a TTI of 20 msec, and information C has a TTI of 10 msec.
In addition, the number of data within the TTI of each information (hereinafter, the number of data within the TTI is referred to as intra-TTI data length) may be arbitrarily selected. In other words, the W-CDMA method allows having different intra-TTI data lengths of a plurality of pieces of information to be multiplexed, even within a same type of radio frames. This allows pieces of information having different QoSs to be multiplexed and transported.
As described above, the W-CDMA method allows the pieces of information having different intra-TTI data lengths to be multiplexed and transported, so that information regarding the intra-TTI data length of each of the pieces of information to be multiplexed needs to be transmitted to a receiving side. Thus, in the W-CDMA method, a Transport Format Combination Indicator (hereinafter referred to as TFCI) is used as information indicating a combination of intra-TTI data lengths of the plurality of pieces of information to be multiplexed so as to be inserted in the radio frame as shown in FIG. 10 and transported.
In other words, as shown in FIG. 10, one frame is composed of fifteen slots, and each of the slots has the plurality of pieces of information to be multiplexed and TFCI inserted therein.
The TFCI indicates the intra-TTI data length of each piece of information by a value of a transport format of each piece of information (normally the number of the transport format). A value of the TFCI is determined with regard to a combination of values of transport formats of the plurality of pieces of information-to be multiplexed.
For example, FIG. 11 shows a case where two pieces of information having different QoS (i.e., information 1 and information 2) are multiplexed, and an exemplary mapping table showing a correspondence between a value of the Transport Format (hereinafter referred to as TF value), which represents the intra-TTI data lengths of the information 1 and the information 2, and TFCI values. TF1 and TF2 represent TF values of the information 1 and the information 2, respectively. In FIG. 11, TF1 shows that the information 1 has sixty-four kinds of intra-TTI data lengths, and TF2 shows that the information 2 has four kinds of intra-TTI data length.
In addition to the use of the TFCI, details of the intra-TTI data length of the TF values TF1 and TF2 of each piece of information and a mapping table as shown in FIG. 11 are notified through a control channel to the receiving side. FIG. 12 shows an exemplary table showing a correspondence between the TF value of each piece of information and the intra-TTI data length thereof in a case of the TF values TF1 and TF2 of the information 1 and the information 2 and the intra-TTI data lengths.
From the description above, the W-CDMA method allows the receiving side to extract the TFCI out of the received data, thereby allowing a TFCI decoder to decode the extracted TFCI to obtain the TFCI value. As a result, the TF value of each piece of information is calculated based on the table showing the correspondence between TFCIs which have been previously acquired through the control channel and the TF values. Then, the table showing the correspondence between the TF value of each piece of information and the intra-TTI data length is used to calculate the intra-TTI data length corresponding to the calculated TF value of each piece of information. Finally, received multiplexed data is divided into the information 1 and the information 2, thereby allowing respective data to be decoded.
The W-CDMA method represents the TFCI as information of 10 bits and has 1024 combinations of TF values for the plurality of pieces of information to be multiplexed. When the number of combinations of TF values for the plurality of pieces of information to be multiplexed may be expressed by 10 bits of less, the TFCIs of the pieces of information are made to have 10 bits by inserting “0” into the most significant bit (MSB) side of the TFCI.
In addition, the TFCI is encoded at a sending side for the purpose of error correction. How to encode TFCI bits in accordance with 3GPP standards will be described as follows.
When information of 10 bits of the TFCI to be inputted into an encoder are assumed to be a9, a8, a7, a6, a5, a4, a3, a2, a1 and a0 (wherein a9 is the MSB and a0 is a least significant bit (LSB)), a code word bi (i=0, . . . , 31) included in an output from the encoder is calculated through an expression (1) shown in FIG. 13. In the expression (1), Mi,n represents a coefficient acquired through the table shown in FIG. 14.
According to the 3GPP standards, the-TFCI stored in one radio frame shown in FIG. 9 has a field of 30 bits. Thus, the code word bi of 32 bits is subject to a puncture processing to delete b30 and b31, thereby obtaining 30 bits. Thereafter, the field of 30 bits is inserted into a TFCI field of the radio frame shown in FIG. 9. Subsequently, data of the radio frame shown in FIG. 9 is subject to a QPSK modulation and further subject to a spectrum diffusion modulation, to then transport the data.
The data in the radio frame as described above is received by a base station or a mobile station (e.g., mobile terminal). Then, the received data is subject to an extraction to extract a TFCI code word from the TFCI field, thereby decoding the extracted TFCI code word as described in the following. Thereafter, the TFCI value of the decoded TFCI code word is checked in order to detect the correspondence between each of the plurality of pieces of information being multiplexed and the intra-TTI data length by referring to the table which has been previously sent from the control channel. The detected correspondence is used as a base for dividing the plurality of pieces of information being multiplexed, to then decode the plurality of pieces of information.
FIG. 15 shows an example of a configuration of a decoding section of TFCI code word. A received signal is subject to an inverse diffusion to collect TFCI code words inserted in the radio frame, then inputting the collected TFCI code words into a de-puncture processing section 1. The de-puncture processing section 1 inserts two “0”s into the last part of the inputted 30 bits of TFCI code word, thereby obtaining 32 bits of TFCI code word. The TFCI code word which has been inserted with 2 bits of “0” is represented as Ri (where i=0, 1, . . . , 31).
The TFCI code word Ri of 32 bits is supplied to a de-masking processing section 2. The de-masking processing section 2 performs a de-masking processing that corresponds to the one using Mi,6 to Mi,9 of the above described coefficients Mi,n shown in FIG. 14. In other words, the coefficients Mi,6 to Mi,9 among the coefficients Mi,n are mask codes and are used by the de-masking processing section 2 for removing a mask. The specific de-masking processing will be performed according to the following procedures of {circle around (1)} and {circle around (2)}.
{circle around (1)} A value is selected which may be a candidate for high-order four bits (a9, a8, a7, a6) of the TFCI corresponding to the mask codes Mi,9. When the TFCI may take values ranging from 0 to 255, for instance, the value of the TFCI may be expressed by 8 bits and thus 2 bits a9 and a8 from the most significant bit of 10 bits of the TFCI is “0”. In this case, a7 and a6 may take “0” or “1” and thus, there are four patterns of high-order four bits of the TFCI.
{circle around (2)} An expression (2) shown in FIG. 13 is used to obtain a value of EX. If the result shows the value EX=“1”, a plus or minus sign of “Ri” is inverted and, if the result shows the value EX=“0”, “Ri” is left as it is. This processing is performed for all of the values of “Ri” where i=0,1, . . . 31.
Next, the data which has been de-masked by the de-masking processing section 2 is subject to a fast Hadamard transformation (FHT) by a fast Hadamard transformation section 3 to obtain a correlation value. The fast Hadamard transformation is a calculation method of efficiently performing a multiplication of the de-masked data and a Hadamard matrix.
The above processing according to the procedures of {circle around (1)} and {circle around (2)} is performed to all possible patterns of candidates of high-order four bits of the TFCI (a9, a8, a7, a6). In the case of the above-described FIG. 11 where the TFCI may take the values ranging from 0 to 225, the candidates of bits a9, a8, a7, a6 may take four patterns as described above and thus, the de-masking processing and the fast Hadamard transformation processing are repeated total of four times. In a case where the TFCI value is 512 or more and all of 10 bits of the TFCI is used, the candidates of bits a9, a8, a7, a6 may take 16 patterns and thus, the de-masking processing and the fast Hadamard transformation processing are repeated total of 16 times.
All of the results of repeating the de-masking processing and the fast Hadamard transformation processing a plurality of times are supplied to a correlation computation section 4. This correlation computation section 4 compares absolute values of all correlation values acquired through the above-described plurality of outputs by the fast Hadamard transformation section 4 to detect a maximum value of the absolute values, thereby obtaining a TFCI value which has been transmitted.
With regard to the TFCI value thus obtained, the mapping table as shown in FIG. 11 which has been previously sent by the control channel and the table shown in FIG. 12 are referred as described above to find the intra-TTI data length of the information being multiplexed, thereby dividing the multiplexed data into each piece of information for decoding.
It is noted that each of the processing sections shown in FIG. 15 may be separately configured as an independent hardware, or a part or the entirety of the processing sections shown in FIG. 15 maybe configured as a Digital Signal Processor (DSP).